This is a tremendous oversimplification. Having personally gotten an explanation for how and who was selected for the trial period from a member of DL upper management, it seems that this initial rollout is as much a test of their systems capacity/readiness as it is a true reward of the top customers. His comment was that too many of DL's HVCs live in certain parts of the country, i.e. hub cities which resulted in them casting a larger net to capture, for now, lower spend HVCs with geographic distribution so that it wasn't just ATL's ability to handle, say car pickup and VIP services but also at smaller, more regional airports. He was also exceptionally clear that there would be some (if not many) who were initially invited who would not make the ultimate cut.

So, for now asking why you didn't get in isn't a conclusive 'you're not getting in'...though we may better be able to evaluate this come spring 2014.